Represents the amount of civil penalties as a part in settlement of litigation.

No definition available.

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Namespace Prefix:	itg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of disgorgement payment as a part in settlement of litigation.

+ References

No definition available.

+ Details

Name:	itg_LossContingencyDisgorgementOfTradingRevenues
Namespace Prefix:	itg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of current or former officers and directors of the company got filed by the company.

+ References

No definition available.

+ Details

Name:	itg_NumberOfCurrentOrFormerOfficersAndDirectorsGotFiled
Namespace Prefix:	itg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount of reserve for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs, which is expected to be paid within one year of the date of the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.25)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 55
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6396582&loc=d3e15243-108350

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Interest expense (income) directly attributable to an award in settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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- Details

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Contingencies - Legal Matters (Details) $ in Thousands			3 Months Ended
Contingencies - Legal Matters (Details) $ in Thousands	Nov. 27, 2015 item	Aug. 12, 2015 USD ($)	Mar. 31, 2018 USD ($)
Contingencies – Legal Matters
Litigation settlement amount			$ 18,000
Settlement costs payable			$ 18,000
Settlement with S E C for Investigation into Proprietary Trading Pilot
Contingencies – Legal Matters
Payment of settlement amount		$ 20,300
Disgorgement payment		2,100
Prejudgment interest		250
Civil penalty		$ 18,000
Case of derivative action captioned Watterson v. Gasser et al.
Contingencies – Legal Matters
Number of current or former officers and directors of the company got filed by the company \| item	11